OracleExtended

Distance Clusters指的是RAC的節點分別放在不同的地方，這些節點可以放在不同的機房，也可以放在不同的城市

主要條件

距離最好小于100KM,兩節點之間要有獨用的光纖專線(國內有案例是租用裸光纖)

主要用途

不適合于全量災備恢復，只適合防范停電，空難，洪水等災難性事故

是否推薦

Oracle更推薦使用本地RAC加dataguard

官方原話如下

頁

Oracle

RAC on Extended Distance Clusters

Oracle

RAC on Extended Distance Clusters is an architecture where servers in the

cluster reside in

locations

that are physically separate. Oracle RAC on Extended Distance Clusters provides

extremely

fast

recovery from a site failure and allows for all servers, in all sites, to

actively process transactions as

part

of a single database cluster. While this architecture creates great interest

and has been successfully

implemented,

it is critical to understand where this architecture best fits especially in

regards to distance,

latency,

and degree of protection it provides.

The

high impact of latency, and therefore distance, creates some practical

limitations as to where this

architecture

can be deployed. This architecture fits best where the

2 datacenters are located relatively

close (and where the extremely expensive costs of setting up direct cables with dedicated

channels between the siteshave already been taken.

Oracle

RAC on Extended Distance Clusters provides greater availability than local

Oracle RAC but it

may

not fit the full Disaster Recovery requirements of

every organization. Feasible separation is great

protection

for some disasters (local power outage, airplane crash,

server room flooding) but not all.

Disasters

such as earthquakes, hurricanes, and regional floods may affect a greater area.

One should

analyze

their situation in order to determine if both sites are likely to be affected

by the same disaster.

For

comprehensive protection against disasters including protection against

corruptions and regional

disasters,

Oracle recommends the use of Oracle Data Guard in

combination with Oracle RAC as

described in the Oracle Maximum Availability Architecture guidelines. Oracle Data Guard

also provides

additional

benefits such as support for rolling upgrades across Oracle versions.

Configuring

an extended distance cluster is more complex than configuring a local cluster.

Specific

focus

needs to go into node layout, voting disks, and data disk placement.

Implemented properly, this

architecture

can provide greater availability than a local Oracle RAC database, but should

be considered

with

Oracle’s Maximum Availability Architecture in mind.

異地RAC的架構

異地RAC的架構如下，兩邊都帶存儲，存儲之間的數據是通過物理主機級別的鏡像實現的，如ASM，兩個存儲分別做鏡像,相當數據都是保存兩份，如A機房的存儲為1T，B機房的存儲也是1T,這個時候主機同時掛載兩個存儲分別做鏡像，相當可用空間還是1T，這樣可以防止單個存儲存在單點故障，中間用光纖相連

架構圖如下

名字解釋

：Dense Wavelength Division Multiplexing密集型光波復用,這是一項用來提高帶寬的激光技術。該技術是在一根指定的光纖中，多路復用單個光纖載波的緊密光譜間距，以便利用可以達到的傳輸性能。這樣，在給定的信息傳輸容量下，就可以減少所需要的光纖的總數量。

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